The freight train is when your having sex in a car, you put the girls head in the window but not to the point where it chokes her, ass in seat, then you put a cigarette with duct tape around her mouth, then every time the male thrusts, smoke comes out of her nose like a freight train
Guy 1: Hey man where you been?
Guy 2: I was just hanging out with Ashley.
Guy 1: Awwshit, did you flip the freight train?!
Guy 2: Nah man, that trains too heavy for me..
Ralph: "so did you and Sally have sex last night?"
Johnny: "Naaah, Sally had a headache last night so I ended up watching porn and waxing the freight train instead."